Optical information processing entails the ability to perform analog operations such as correlation, convolution, and differentiation with optical beams. These operations provide results that are both positive and negative in value. Since the intensity of an optical beam is always positive, positive and negative values are sometimes represented as the difference in power between two optical beams. Various methods are known for processing such pairs of optical beams having an analog value determined by the difference in their power. Examples of such methods are described by Miller in IEEE J. Quantum Electron., Vol. 29, Number 2, February 1993, pages 678-698. One limitation of these methods is that because of unavoidable attenuation of optical beams in optical systems, the analog value represented by the difference in power of the optical beams is also attenuated.